1. Field of the Invention
The present invention relates generally to packet switched local area networks, and specifically to call transfer mechanisms within packet switched local area networks.
2. Background of the Present Invention
Different multi-media standards have been defined for different types of systems in which the underlying transport is a Packet Based Network implementing voice over Internet Protocol (IP). For example, for Integrated Services Digital Networks (ISDN), the H.320 and H.324I/M standards are utilized. In addition, H.324 standards apply to Public Switched Telephony Networks (PSTNs), whereas H.324M standards apply to Public Land Mobile Networks (PLMNs). Furthermore, for Local Area Networks (LANs), the H.323 standards are used.
Within H.323 systems, H.323 endpoints may be integrated into personal computers, implemented in stand-alone devices, such as wireline or wireless telephones or implemented in wireless telecommunications systems. H.323 endpoints advantageously provide real-time audio, video and/or data communications capabilities in point-to-point or multipoint conferences.
Each H.323 endpoint is registered with a Gatekeeper for the H.323 system. The Gatekeeper stores an IP to that H.323 endpoint is requested, the Gatekeeper knows how to route the connection. If the H.323 endpoint is a Mobile Station (MS), such as a cellular telephone, the IP address for the MS typically includes the IP address for a Mobile Switching Center (MSC) serving the MS for call signaling.
H.323 systems currently support call transfer services, which allows the transferring end-point, which is the party that has one held call and one active call, to connect the remote end-points of the two calls and disconnect itself. The protocol used by the H.323 network for the call transfer function is specified by H.450 standards. In the H.450 solution, after the transferring end-point invokes call transfer, the original two calls are released and a new call is established between the transferred end-point and the transferred-to end-point.
Once the transferring end-point transfers the call, if both the transferred end-point and transferred-to end-point are within the H.323 system, the speech and/or data (commonly referred to as the media stream or media packets) are routed directly between the transferred end-point and transferred-to end-point. This requires both the transferred end-point and the transferred-to end-point to change the address of sent packets from the transferring end-point's address to each other's address. In order to accomplish this, both the transferred end-point and the transferred-to end-point must have knowledge of the call transfer and have the ability to perform the address switch. Implementing part of the call transfer functionality within the H.323 end-points themselves is neither efficient, nor desirable.
In addition, the H.450 solution is extremely difficult to implement when either the transferred subscriber and/or the transferred-to subscriber are within another system, such as the PLMN/PSTN. Since the PLMN/PSTN does not support H.323 protocols, when the transferred and/or transferred-to subscriber belongs to the PLMN/PSTN, the H.450 standard will not be supported by these subscribers.
Therefore, in order to perform call transfer when one or both of the remote parties is within the PLMN/PSTN, the H.323 network must intercept the H.450 messages and simulate end-point behaviors in the Gateway that is responsible for PLMN/PSTN and H.323 interworking. For example, if the transferring subscriber (hereinafter referred to as the A subscriber) is within the H.323 network and both the transferred subscriber (hereinafter referred to as the B subscriber) and the transferred-to subscriber (hereinafter referred to as the C subscriber) are outside of the H.323 network, after subscriber A transfers the call, the speech and/or data from subscriber B is routed to the Gateway. The Gateway must have knowledge about the call transfer and must route the speech and/or data to subscriber C. Similarly, the speech and/or data from subscriber C is routed to the Gateway, and the Gateway must route the speech and/or data from subscriber C to subscriber B. Thus, with the current H.450 standard, the Gateway must include the end-point functionality for H.450 call transfer handling. It is neither desirable, nor efficient, to require Gateways to include part of the call transfer functionality.
It is, therefore, an object of the present invention to route the media packets through the transferring end-point after the call is transferred between the transferred and transferred-to end-points.
It is a further object of the present invention to enable the transferring end-point to be free to make other transactions after call transfer.